1.在dataSource赋值的时候：
注：model.mediumArr为加载进来的新数据源
NSMutableArray*indexPaths = [[NSMutableArray alloc] init];
for ( inti =0; i < model.mediumArr.count; i ++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForRow: self.dataSource.count+ i inSection: 0];
[indexPaths addObject: indexPath];
}
if (indexPaths.count > 0) {
[self.dataSource addObjectsFromArray:model.mediumArr];
[self.collectionView insertItemsAtIndexPaths:indexPaths];
[UIView performWithoutAnimation:^{
[self.collectionView reloadItemsAtIndexPaths:indexPaths];
}];
}
2.如果项目涉及到collectionView的滑动优化，在需要只调用reloadData的时候：添加如下动画。
[UIView animateWithDuration:0 animations:^{
[self.collectionView performBatchUpdates:^{
[self.collectionView reloadData];
} completion: nil];
}];
